Circuitry for recognizing two-tone compound signals in telephone

Details Circuitry for recognizing two-tone compound signals in telephone Circuitry for recognizing two-tone compound signals in telephone

1988-03-25

1990-05-01

Ng, Jin F.

Telephonic communications

Supervisory or control line signaling

Signal receiver

379283, 34082573, H04M 150

Patent

active

049225286

ABSTRACT:
A circuit is described for recognition of two-tone compound signals of two frequency ranges (F1 to F4, F5 to F8) in telephone installations with a limited transmission band width. Band pass filters (11, 12) whose output signals are added up and weighted individually are provided in a number corresponding to the number of possible single tones. The weighted output signals are each compared with the output signal sum of one of two frequency ranges (F1 to F4, F5 to F8 ) in order to signal a valid single tone. To increase the certainty of speech, another summand (Su, So) that is derived from a summation of the output signals of at least two other band pass filters (13) whose mid-band frequencies (F9 to F11) are outside the two frequency ranges (F1 to F4, F5 to F8) is also sent to the summation circuit.

REFERENCES:
patent: 3649771 (1972-03-01), Flowers
patent: 4042788 (1977-08-01), Richards
patent: 4107475 (1978-08-01), Carlquist et al.
"Add DTMF Generation ane Decoding to DSP-.mu.P Designs" P. Mock, EDN Mar. 21, 1985, pp. 205-220.

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